AAPG Foundation Funded Distinguished Lecture Examples of salt tectonics from the West African passive margins: Exploration in a major emerging petroleum province Gabor C. Tari Vanco Energy Company Houston, Texas (c) 2001 The American Association of Petroleum Geologists and Gabor C. Tari. No slides, figures, text or other matter contained herein may be reproduced without the written permission of both the American Association of Petroleum Geologists and Gabor C. Tari. OUTLINE Introduction Morocco/Mauritania Senegal/Guinea Bissau Equatorial Guinea/Gabon Congo/Angola Classification of toe-thrust zones Syn-rift versus post-rift salt Exploration implications Conclusions Acknowledgements 3.6 Mid-Norway 0,6 3,0 Major Deep Water Basins & Discovered Reserves Faroes Total: 34.7 MMBO/C + 106 TCF White Zone Scotian & WoS Jeanne D’Arc So. Caspian Sakhalin Italy 3,0 Morocco 12 8,6 Egypt 2,0 0,9 Trinidad 2.0 1,8 2.7 US GoM NW & SE Borneo Taumalipas Nigeria & Campeche Eq. Guinea Gabon 0,5 Congo Tanzania Angola Brazil 13 NWS & ZOCA 12,4 0,9 7 0,1 Mozambique 12 6,8 10,9 Recoverabe S. Africa Resources in BBOE AREAS OF PROSPECTIVE DEEPWATER BASINS Total discovered deep water (>500m ) recoverable resources per region, announced as of January 2001. These resources include producing reserves, those in development, and technically recoverable resources for which development has not been sanctioned. Pettingill and Weimer, in press REGIONAL TRANSECTS Syn-rift salt basins: Morocco, Mauritania Senegal, the Gambia Guinea Bissau Post-rift salt basins: Cameroon, Equatorial Guinea, Gabon, Congo, Angola MOROCCO Regional transects a b Safi Haute Mer Ras Tafelney SENEGAL, THE GAMBIA, GUINEA BISSAU Regional transects Dakar Offshore Profond Guinea Bissau Schematic Restoration Offshore Profond Dakar, Senegal REGIONAL TRANSECTS Syn-rift salt basins: Morocco, Mauritania Senegal, the Gambia Guinea Bissau Post-rift salt basins: Cameroon, Equatorial Guinea, Gabon, Congo, Angola Corisco Deep, Equatorial Guinea Astrid/Anton Marin Gabon Corisco Deep, Equatorial Guinea Astrid/Anton Marin, Gabon Lower Congo, Kwanza and Benguela basins, Angola Regional Top Salt, Angola 5x vertical exaggeration view towards the NE Lower Congo, Kwanza and Benguela basins, Angola Regional Bathymetry Regional Top Salt Block 17 Block 33 Block 18 Block 34 Block 19 CROSS-SECTIONAL ASYMMETRY IN TURTLE STRUCTURE GROWTH (Mauduit and others, 1998) SEISMIC EXAMPLE, BLOCK 18 NW SE TWO-WAY TRAVELTIMEINSECONDS CHANNEL C 3 CHANNEL B CHANNEL A 4 Experiment by Bruno Vendeville, AGL, Austin, Texas Experiment by Bruno Vendeville, AGL, Austin, Texas INFLUENCE OF TURTLE STRUCTURE GROWTH ON SEDIMENT DISPERSAL Lower Congo Basin, Angola Qualitative classification of toe-thrust zones in African salt basins Lower Congo Basin, Angola Sequential restoration, Lower Congo Basin, Angola EXPLORATION IMPLICATIONS • The toe-thrust zone provides very attractive structural targets and generally the fold-train provides the first structures out-of-the-basin where hydrocarbons are generated. • The toe-thrust zone in a syn-rift salt setting appears to create more dormant structures as opposed to the highly efficient post-rift salt case where the structural traps tend to be redeformed continuously which may lead to the loss of hydrocarbons. • The salt-cored foldbelt may not always be present and it develops only when the original salt is fairly continuously distributed and its thickness decreases gradually towards the original basinward pinchout. CONCLUSIONS • Exploration experience gained in specific salt basins of West Africa may not be directly applicable to other salt basins along the entire passive margin. • Regional-scale similarities of the salt basins include the progressive complication of salt-related structures basinward, the change from an extensional domain in the shelf to a compressional domain in the slope, and the presence of a toe-thrust zone at the oceanward edge of the basins. • Regional-scale and perhaps prospect-scale differences are partly attributed to the relative stratigraphic position of the salt in relation to the rifting of the margin. ACKNOWLEDGMENTS AAPG AGIP BP AMOCO First Exchange LASMO SHELL TotalFinaElf VANCO WesternGeco.